The present invention relates to blades intended to be mounted on an arbor or output shaft of equipment such as rotary trimmers and brush cutters, and in particular relates to such blades constructed to include an integral skid plate and to resist having fibrous material accumulate and become wrapped about such a blade or its drive shaft.
Rotary blades previously known for use on portable trimmers and brush cutters, similar to blades for rotary lawn mowers, have been substantially planar, as shown in blade B in FIG. 1. Such blades include cutter portions having sharpened edges, or wires or plastic filaments extending outwardly from radially outer portions of the blades. Such blades have been useful in trimming grass but have performed less satisfactorily in trimming heavier vegetation such as blackberry canes.
Additionally, such blades on trimmers and brush cutters have been subject to damage or to being dulled by accidentally encountering the surface of the ground in which vegetation is growing, unless tools equipped with such blades have also been equipped with devices such as hollow, cup-like spacers, as shown at S in FIG. 1, extending axially from the shaft on which such blades B are attached, to keep such blades spaced apart from an adjacent surface such as the ground.
Such previously available rotary blades are subject to having grass become wrapped around the drive shaft on which the blades are mounted, thus wasting power actually needed to rotate the blades and periodically requiring the equipment to be stopped and cleaned.
What is desired, then, is an improved blade for use on trimmers, brush cutters, and other rotating shaft equipment, which can be used effectively to cut vegetation to a desired height and to cut portions of such vegetation into pieces effective for use as mulch, and which will perform effectively with significantly less accumulation of fibrous materials wrapped about the driving shaft and otherwise fouling the rotary equipment on which such a blade is to be used.
As an answer to the above-described needs and to the shortcomings of the prior art, the present invention provides a rotary blade for a trimmer or brush cutter, in which a cup includes a hub portion and a concentric cup wall that extends to an annular crown from which a concentric outer skirt extends axially opposite the direction of the cup wall, to protect the arbor-and the point of attachment of the rotary blade to its driving shaft, and in which a plurality of cutters extend outward from the outer skirt, at locations spaced apart from the annular crown in the direction toward the hub portion.
In one preferred embodiment of the present invention a rotary blade has a central hub portion that lies in a first plane, from which a cup wall extends to a crown lying in a parallel second plane, and an cuter skirt extends oppositely from the crown to a third plane parallel with the first and second planes and located, preferably, so that the first plane is between the second and third planes.
In one preferred embodiment of the present invention several cutters extend radially outward from a margin of the outer skirt, and the hub, the cup, the outer skirt, and the cutters are all included in an integral structure.
In one preferred embodiment of the present invention, each of the cutters has an outer tip and at least one of the cutters is shaped so that the outer tips of different cutters rotate about a central axis of rotation of the rotary blade in at least two and preferably three different planes.
In one embodiment of the invention slender flexible cutters are attached adjustably to the outer skirt portion of the rotary blade.
In one embodiment of the invention such flexible cutters may be of a polymeric resin monofilament material and may be attached to the skirt by being inserted through a set of through-holes small enough and located close enough to each other to hold such a piece of monofilament frictionally.
In one embodiment of the invention both fixed, sharpened solid cutters and flexible cutters extend outward from the outer skirt.